Blood coagulation analyzers are known which prepare an analysis sample by adding a blood-coagulating reagent to a blood sample, and analyze the coagulation time of the blood by optically measuring the process of a coagulation reaction in the analysis sample. For the sake of generality, such an analysis sample made by adding a reagent to blood or made in any other manner may be referred to as a blood coagulation analysis sample.
In blood coagulation analysis, interference substances such as hemoglobin, bilirubin chyle and the like present in the analysis sample (substances that optically interfere with the measurement of a target material and coexist in the sample together with the target material (for example, fibrinogen) being examined) may influence the optical measurement and hinder accurate analysis.
When measurement is performed using long wavelength light (for example, 800 nm), hemoglobin and bilirubin do not affect the measurement and chyle only slightly affects the measurement, however, measurement sensitivity is low.
Furthermore, the coagulation reaction changes the amount of light transmitted through the sample material, the change is proportional to the amount of coagulation factor (for example, fibrinogen) contained in the analysis sample. Therefore, there is little change in the amount of light in an analysis sample that has a low coagulation factor content, and accurate analysis can not be performed under long-wavelength light that has low measurement sensitivity.
Therefore, in conventional blood coagulation analyzers use light at a wavelength in the vicinity of 660 nm for measurement to obtain suitable sensitivity wherein the interference substances do not influence very much so that the analyzers can perform analysis adequately.
Conventionally, the interference substances present in a sample (serum and the like) are measured prior to performing the main measurement (for example, biochemical analysis) (for example, refer to Japanese Laid-Open Patent Publication Nos. S57-59151 and H06-66808, and U.S. Pat. No. 5,734,468).
In the measuring method for degree of chyle, jaundice and hemolysis in serum disclosed in Japanese Laid-Open Patent Publication No. S57-59151, serum is irradiated by light at four wavelengths, and light absorption is primarily measured using short-wavelength light within the visible range (for example, 410 nm), and a serum sample that has measured light absorption greater than a fixed value is determined to be abnormal due to chyle and jaundice and hemolysis. Then, secondly the serum sample that has been determined to be abnormal is subjected to determination of the degree of chyle, jaundice, and hemolysis by comparing the light absorption measured at four wavelengths with several preset standards.
In the chromogen (interference substance) measurement method disclosed in Japanese Laid-Open Patent Publication No. 6-66808, a sample blank liquid is prepared by mixing a blank reaction reagent with a specimen including suspension material (hemoglobin, bilirubin, chyle and the like), and measuring the degree of interference substance by irradiating the sample blank liquid with light at four wavelengths that include a wavelength at which the light is absorbed by chyle, and substantially not absorbed by hemoglobin and bilirubin. Specifically, the degree of chyle is calculated by assuming the degree of absorption represented by an exponential function of the wavelength, and determining a wavelength-absorption regression curve. Moreover, the amounts of hemoglobin and bilirubin are calculated by assuming a preset fixed relationship between absorptions at different wavelengths, and preparing and solving simultaneous linear equations related to the optical absorbance at the measurement wavelength.
In the analyzer for determining the presence of hemolysis, jaundice, and lipemia in a serum sample disclosed in U.S. Pat. No. 5,734,468, the optical absorption of a serum sample in a needle tube is first measured by irradiating the serum sample aspirated into the needle tube disposed in a transparent part provided with a probe using light emitted from light emitting diodes. Then, a serum sample that has been determined to be measurable based on this optical absorption is transferred to a clinical analyzer where a main measurement is performed.
In the conventional blood coagulation analyzers described above, the measurement wavelength is set with regard to the possibility that a sample contains interference substances. However, there are various contents of interference substances and coagulation factors depending on the sample, and the optimum wavelength for measurement will vary sample by sample. Therefore, conventional blood coagulation analyzers can only measure at preset wavelengths, thus reducing analysis accuracy.